The present invention is directed to developments in the dental field, with particular regard to dental restoration apparatus. Typically, apparatus of this type includes a prosthetic implant, an abutment and a fastener apparatus. In use, the implant is adapted to be implanted within an anchor site fashioned within the bone of the jaw of a patient. The abutment is adapted to be mounted on the implant to provide a support surface for a tooth restoration. And, the fastener apparatus functions when engaged with both the implant and abutment in a mounted orientation to secure the structures in a manner to positively resist relative movement of the abutment and implant both axially and rotationally.
It is common practice in dentistry and dental surgery to use a prosthetic device characterized as an implant to serve as a base to support a tooth restoration in the process of replacing a natural tooth lost for some reason. In this practice the implant is imbedded in a site referred to as an anchor site created in the bone within the jaw of the patient. It is hoped that the implant, during a healing process, will become secured to and integrated with living bone cells juxtaposed thereto, thus becoming immobilized within the anchor site.
Implants of the prior art have been designed variously in order to achieve a level of securement during a process of biological cementation, known as xe2x80x9cosseointegration,xe2x80x9d when the implant attaches to and integrates with living bone cells in position in situ within the anchor site. Generally, the implant includes a body formed either of circular cross-section or of gradually tapered outline from a trailing end toward a leading end. It is intended that implants fabricated in these body shapes when received in the anchor site become immobilized in the seated, final disposition to function as a final, stable and secure base for mounting an abutment and tooth restoration.
Many prior art designs of dental restoration apparatus and its component parts function adequately in carrying out the intended use. However, many designs of implant are known to suffer from a number of well documented difficulties and shortcomings that continue to require attention of those involved in the art of tooth restoration.
Many of these difficulties and shortcomings are attendant to factors including the consequences of and the reaction to the force of loading upon the implant/abutment interface during the initial or integration phase, particularly with forces such as those generated during eating, and the consequences of and the reaction to the lack of adequate surface area of the body of the implant in contact with viable tissue and bone cells within the anchor site.
Another difficulty and shortcoming has its genesis in the placement of threaded implants in dense or poorly vascularized bone, or in loose, poorly organized bone with excess fatty bone marrow. In the former, the pressure of threading an implant into a tapped, dense, hard bone may cause pressure necrosis at the implant bone interface, resulting in failure or a total loss of the implant due to bone necrosis and subsequent fibrous integration of the implant to the bone. In the latter case, implants threaded into bone of poor quality, such as loosely organized bone with fatty bone marrow generally are inadequately stabilized. The inadequacy of stabilization will subsequently lead to failure of the implant.
The body surface of the body of many implants of the prior art is smooth throughout. This is the case irrespective of whether the implant is of circular cross-section or of a configuration tapered from a trailing toward a leading end. The implant of each configuration is pressed fit into the anchor site to the final, seated disposition. Thus, the anchor site within which the body is received is specially fashioned to accommodate the implant whatever the size of the body and whatever its outline. If the anchor site is not properly sized problems will occur. For example, if the anchor site is oversized, the implant will not be supported properly during the healing process. Any movement of the implant when subjected to a force, such as a loading force acting at the implant/abutment interface during the initial healing or integration phase, or within another location during chewing or other oral functions will impede the process of osseointegration. On the other hand, if the anchor site is undersized, the body of the implant likely will cause damage to the cellular bone structure within the anchor site as the implant is pressed fit or threaded (screwed) to the final, seated disposition. Damage represented by crushed bone and fibrous tissue formation should be avoided as best as possible. Thus, the dentist or dental surgeon strives to fashion an anchor site to a size that closely tolerates movement of the implant during implantation, and presents a maximum amount of surface area within the wall of bone that ultimately will reside in intimate contact with the surface of the body of the implant. Adverse characteristics, including those that are the resultant of a poorly prepared anchor site, a poor quality of bone within the anchor site and/or any capability of movement of the implant during healing must be reduced substantially or totally eliminated.
The consequences of loading evidence themselves rather dramatically.
In the past, implants were used by dentists and dental surgeons as anchors for denture/bridge constructions for replacement of multiple, natural teeth. The prior art included implants specifically designed and generally suited for that purpose. Recently, however, dental professionals are being asked to respond to requests related to other aspects of dental surgery, namely that of replacement of individual teeth with tooth restorations that appear more like the natural tooth that was lost. Prior art implants, typically, were fabricated with a body providing only a few millimeters of interface diameter for support of a crown or other restorative structure. The range may be 4 mm or less measured between the occlusal margins. It is not unusual, however, for the dentist or dental surgeon to work with a crown or other restorative structure having an occlusal loading surface much larger in interface diameter. For example, the occlusal loading surface of a molar is in the range of about 6-7 mm by 10-12 mm. Oftentimes, failure and resultant breakdown occurs at the interface of implant and abutment. This may be evidenced by a ditching effect around the cervical margin of the implant, a resultant or associated bone loss, and a loosening or fracture of the body of the crown or tooth structure.
Still further, the emergence profile of the crown as it comes through the gum tissue generally is not aesthetically pleasing. This is because the large size of crown associated with a small diameter implant has an unnatural appearance. Furthermore, periodontal disease may develop as a result of the unnatural undercut of the relatively large crown as it tapers to meet the relatively small body of implant.
In addition, fastener assembies used in prior art to connect the implant and abutment and, then, maintain the connection so that the abutment cannot loosen itself from the condition of engagement with the implant suffer from various difficulties and shortcomings. If the fastener assembly is incapable of maintaining integrity between the abutment and implant, the prosthesis can be damaged, and possibly require replacement. In addition, the loss of integrity of the connection between abutment and implant resulting in microvibratory movement of structures and deterioration of bone cells and tissue within and around the anchor site will encourage a growth of bacteria, leading to gum disease. The effect is cervical bone loss around the neck or shoulder of the body of the implant, and ultimately bone loss along the longitudinal length of the body.
Threaded fasteners, such as screws and bolts for securing workpieces together are well known in the art and have been utilized in a wide variety of applications. Some fasteners are useful since they may be selectively secured and released, as may be required. However, many screws and bolts of this type suffer from one or more shortcomings. One shortcoming, the resultant of conditions of mechanical vibration, manifests itself by a tendency of the screw or bolt to loosen or xe2x80x9cback outxe2x80x9d from one or the other or both workpieces over time.
In order to address this problem, lockwashers and locknuts of well known design have been developed for use in concert with the screw or bolt. Other mechanical elements, such as a fastening element with a slotted conical sleeve disclosed in U.S. Pat. No. 4,370,082 to Sandberg, and a screw fastener with a concentrically disposed O-ring disclosed in U.S. Pat. No. 5,12,839 to Ingber et al have been developed to meet a need.
Currently available lockwashers and locknuts function effectively but they have their drawbacks. To this end, lockwashers tend to be unsightly. Accordingly, lockwashers are not suited for, and tend not to be used in, applications placing emphasis on the aesthetics of the workpiece connection. Locknuts including a nylon walled bore generally only provide reliable locking action the first time they are used. Accordingly, locknuts are not a preferred mechanical element when the fastener is to be reused.
The structure in the form of a slotted conical sleeve, disclosed in the Sundberg patent, generally is limited in use in mounting objects in hard materials such a stone, brick, plaster, concrete or the like, and holding the fastener in the material by frictional force. Again, the application or use of the conical sleeve is limited, and generally only reliably effective for a onetime use application.
Finally, the screw fastener with the concentric O-ring, disclosed in the Ingber et al patent, is not appropriate for certain applications where the resilient rubber of the O-ring would deteriorate or have a tendency to deteriorate during use in the particular environment over time.
Accordingly, a need currently exists for an improved fastener assembly providing greater versatility, reusability and a longer service life. A need also exists for an improved implant and abutment providing the same goals.
The present invention in the field of dental implantology is considered not only to address but successfully satisfy desires and demands of the patient regarding dental restoration apparatus. To this end, the structure of the invention has been found to permit immediate or early loading of an implant once received within an anchor site in the jawbone of the patient. In addition, the structure of the invention has been found to enhance the capability of bone integration with the implant to effectively accelerate the time between placement of the implant and that of actual loading of the implant with a final restoration. Thus, the invention recognizes the desires and demands directed to the practice of dental implantology by providing an extremely stable implant and permitting early or immediate loading without resultant breakdown.
Accordingly, it is an object of the present invention to provide a dental restoration apparatus including an implant, abutment, and a fastener assembly that overcomes the shortcomings, limitations and disadvantages of the prior art briefly discussed above.
Another object of the present invention is to provide the body of an implant with a pattern including one or more projections characterized as xe2x80x9cflutesxe2x80x9d extending along the body of the implant to substantially increase the surface area of contact between bone tissue and implant within the anchor site. It is intended that the implant once the process of implantation is completed and the healing process runs to completion, will secure to and integrate with the bone tissue within the anchor site in a more positive manner and provide a more secure base for other components of the dental restoration apparatus. The increase in a capability of securement is considered to follow the cutting action of each flute into the wall within the anchor site and into bone tissue during pressed fitting of the implant to a final, seated position. The increased surface area from tip-to-tip along the pattern of flutes remains in contact with the bone during healing. Not only is the surface area of the body when compared with an implant otherwise of like construction increased by a factor of about 50% or more the pattern of flutes adds stability to the implant to assist in osseointegration.
A further object of the present invention is to form the body of an implant in a circular cross-section along substantially its entire surface from the trailing end to the leading end, and provide the body with a pattern of one or more flutes, as discussed in the immediately preceding paragraph. The pattern of flutes that increases the surface area of the implant permits use of an implant in a tooth restoration process is of smaller cross-sectional dimension than an implant otherwise considered for use.
Still another object of the present invention is to form the body of an implant with a leading end of a first cross sectional dimension and a trailing end with an enlarged shoulder. The structure of the implant throughout its leading end minimizes the need for bone removal within the anchor site to maximize the quantity of viable bone cells available around the anchor site. The enlarged shoulder that locates within a counterbore of less depth provides a larger surface for receiving the components of the dental restoration apparatus, to better distribute a load that may be placed upon a restorative crown during chewing.
An additional object of the present invention is to provide an improved fastener assembly including a fastener member and sleeve capable in use in connecting the other components of the dental restoration apparatus in a manner preventing movement of the components. Movement is prevented axially through mechanical compression and rotationally through a friction member acting between components.
Yet another object of the present invention is to provide a fastener assembly of relatively simple and inexpensive construction that not only is versatile but also useful in its application over an extended period of time and multiple uses.
Yet another object of the present invention is to provide a fastener assembly of the above construction appropriate for applications where the fastener member must be loosened or removed periodically. To this end, the fastener assembly advantageously functions over a long service life frictionally.
Additional objects, advantages and other novel features of the invention will be set forth in part in the description that follows. Other objects and advantages will become apparent to those skilled in the art upon examination of the text and/or realized and obtained by consideration of the instrumentalities and combinations particularly pointed out in the appended claims defining the scope of the present invention.
The preferred form of the invention in a dental restoration apparatus includes an implant having a body of substantially solid construction fabricated in a circular outline from a trailing end at a mounting surface substantially to the leading end. The implant further includes a pattern including one of more flutes along the surface of the implant extending between the leading and trailing ends in an attitude substantially parallel to an axis through the body. In the preferred embodiment, the pattern includes a plurality of flutes arranged equidistantly around the body,. Each flute includes a tip that functions as a cutting instrumentality when the implant is pressed fit into an anchor site. Each flute, therefore, cuts into the bone tissue as the implant is moved in the seating direction, and remains within the cut to better stabilize the implant during healing.
In another form of invention, the dental restoration apparatus includes an implant having a body and an enlarged shoulder at a mounting surface at a trailing end. Additionally, the dental restoration apparatus includes an abutment having a body and a mounting surface at a leading end adapted to move into a generally coplanar relation with the mounting surface of the implant. Preferably, the mounting surfaces have mating, interlocking profiles preventing relative rotation between the implant and abutment when mounted together in a positional adjusted location.
In yet a further form of the invention, the body of the implant may have a diameter of between substantially 3.5-4.0 mm and a shoulder and mounting surface of a diameter somewhat larger in size. Advantageously, the relatively small body dimension allows the surgeon to minimize bone removal within the anchor site. Consequently, a larger area of viable bone cells remain adjacent the anchor site. The shoulder of enlarged diameter is considered to support the crown and distribute the load and stress generated during mastication over a larger surface area. A radiused transition shoulder connecting the mounting surface and body also reduces stress, more evenly distributes the load and provides a stable seat for the implant that resists rocking that could otherwise lead to bone loss and loosening of the implant over time from the in situ residence position within the anchor site.
In addition, to achieve the foregoing and other objects and in accordance with the present purposes and aspects of the present invention as described herein, an improved fastener assembly is provided for engaging and positively resisting loosening from at least a pair of workpieces. These workpieces comprise an implant and an abutment of the dental restoration apparatus. The fastener assembly comprises a fastener member including a head and an elongated body extending from the head to a distal end. The elongated body has a first diametrical dimension D and is threaded over a portion of its length from the distal end toward the head. The fastener assembly also comprises a sleeve member formed of resilient material circumferentially received about the elongated body. The sleeve member includes an inner and outer surface and a slit through both surfaces from end-to-end creating opposed, spaced-apart, confronting surfaces throughout the full length of the sleeve. The diametrical dimension of the outer surface is S (wherein S greater than D). In addition, the fastener member includes means for compressing the sleeve member so that the sleeve compressively engages against the elongated member to bind the fastener assembly against loosening from the workpieces as the fastener member is tightened.
The compressing means may be a protuberance or series of protuberances formed on the outer surface of the sleeve member in a midpoint location between its ends. Each protuberance provides a focused pressure point to deform the sleeve from a relaxed condition and bind against the fastener member, thereby preventing loosening as a result of vibration propagated through the workpiece and the fastener assembly.
Preferably, however, the compressing means is comprised of an outward bow in the inner and outer surfaces of the sleeve member at the midpoint between its ends, around the sleeve from one confronting surface to the other confronting surface. Similarly, the outward bow provides a focused pressure point and similar action-reaction of during deformation.
In a more specific definition, the fastener member includes an elongated body that may take the form of a screw. The fastener member further includes a second portion in the form of a channel extending from a shoulder at the end of the threaded length toward the head. The channel has a diametrical dimension D1 (wherein D1 less than D). The inner surface of the sleeve member has a diametrical dimension S1 (wherein D greater than S1 greater than D1). As the screw is tightened into a workpiece/abutment, the outer surface within the region of the protuberance/outward bow engages the wall of an aperture. This causes the sleeve member to deform and compress inwardly from a relaxed condition further into the channel and into frictional engagement along the base of the channel. The memory of the material of the sleeve member, however, exerts an outward pressure thereby pressing the sleeve member against the wall of the aperture. This frictional engagement between the sleeve member and wall of the aperture functions in conjunction with the movement of the sleeve member into the channel to provide a positive holding force that resists loosening of the fastener member.
The fastener assembly of the present invention has a long service life. The fastener member, in fact, is reusable, effectively functioning throughout its life to positively resist loosening equally well on the first and subsequent uses. Aesthetics are of no concern since the structure of the fastener member is hidden from view within the workpiece/dental restoration.
Finally, In a preferred form of the invention the fastener is formed by a member including an elongated body with a head at one end and thread extending from the opposite end toward the head. The threaded length has a first diametrical dimension. A channel of a second, smaller diametrical dimension is located between the head and threaded portion. The fastener also includes a sleeve of resilient material received within the channel. The sleeve has an inner and outer surface, and slit though the surfaces forming opposed, spaced-apart confronting surfaces. The outer surface of the sleeve has a diametrical dimension greater than that of the threaded length so that the outer surface of the sleeve in a relaxed condition extends outward of the channel. Finally the sleeve includes an outer circular bow in the outer surface to exert a force in compression to deform the sleeve into a tight frictional engagement within the channel.
Still other objects of the present invention will become apparent to those skilled in this art from the following description, claims and drawings that illustrate and describe a preferred embodiment of the invention together with the best mode suited to carry out the invention. As it will be realized, the invention is capable of other different embodiments and its several details are capable of modification in various, obvious aspects all without departing from the spirit of the invention. As such, the drawings and descriptions thereof should be regarded as illustrative in nature and not as restrictive.